In the case where there is a large difference in power consumption between the daytime and the nighttime or in the case of a power system with numerous interconnected wind power plants whose power generating capability varies depending on the wind condition, there is needed a power storage apparatus which stores surplus power in the nighttime or the like and discharges electricity during the daytime when the power goes short to correspond to a peak load, so as to effectively utilize a power generation facility. The most representative one is a pumped storage hydroelectric plant. In this plant, water is pumped to an upper dam during the nighttime to effectively store surplus power during the nighttime, and power is generated with a hydraulic turbine generator using the stored water in the daytime hours when a large power is consumed, so as to correspond to the peak load during the daytime.
The pumped storage hydroelectric plant has good responsiveness as a large power generation facility, and thus assumes the central role of equalizing loads of power systems. However, the power storage technology using the pumped storage hydroelectric plant is limited in geographical conditions such as whether it is possible to use a river or seawater, whether it is possible to build a dam, and so on. There is a further limitation that it is not applicable unless the input/output capacity of the system is 200 MW at the minimum.
As a relatively large power storage facility other than the pumped storage hydroelectric plant, power storage apparatuses using hydrogen are known. It is known that a power storage apparatus which includes electrolyzing and power generating means having a solid-oxide electrolyte and combines a steam electrolysis cell and a fuel cell. A solid electrolyte fuel cell can generate power by adding oxygen and hydrogen. Further, as backward reaction, it is also possible to apply voltage to the added steam to electrolyze it for obtaining oxygen and hydrogen. Utilizing this principle, steam is electrolyzed by surplus power to produce hydrogen, and the hydrogen is utilized to generate power when power is needed.
A common heat storage technique is known. It is known that an apparatus such that waste heat at 200° C. or lower is stored in a latent heat storage material such as sodium acetate 3-hydrate or magnesium chloride 6-hydrate, and heat is exchanged between the latent heat storage material and a heat medium for utilizing the waste heat. A heat storage technique applied to solar power generation is known, in which molten salts corresponding to respective temperatures of 649° C. or higher, 816° C. or higher, 927° C. or higher, and 982° C. or higher are used as a heat storage material. It is known that a heat storage unit in which a molten salt as a heat storage material is filled in a porous ceramic container.
In power storage apparatuses using hydrogen, heat which is generated mainly during power generation is utilized effectively, and it is important how to supply heat required for electrolysis. Heat obtained mainly during power generation is used for air conditioning. However, in an air conditioner application, heat can be supplied only in the vicinity, and demands for air conditioning do not always match the generated heat amount. Thus, the heat cannot always be utilized effectively. It is known that heat generated during power generation is stored in a heat accumulator, and the stored heat is used for generating hydrogen. Also in this case, it cannot be said that use efficiency of heat generated during power generation is always high.
Incidentally, in a power storage apparatus or a heat storage apparatus, ceramic members are used which excel in heat resistance, strength, toughness, and so on. Further, ceramic members are used in various apparatuses as a heat resistant member, abrasion resistant member, an abrasive, a precision machine member, and so on. In recent years, application mainly of nonoxide-based ceramic members of a silicon carbide (SiC), a silicon nitride (Si3N4), and the like is in progress to semiconductor manufacturing apparatus parts, parts for energy equipment of nuclear energy or a gas turbine, space structural parts, automotive parts such as engine parts and exhaust gas filters, heat exchanger parts, pump parts, mechanical sealing parts, bearing parts, sliding parts, and so on.
Ceramic members generally contract about 20% during sintering, and hence it is difficult to fabricate large parts and complicated shape parts with them. Accordingly, attempts have been made to prepare a plurality of ceramic members and couple them together to produce a large part or a complicated shape part. As a method to join ceramic members together, there has been proposed a method to join a plurality of ceramic members by using reaction sintering of a silicon carbide.
It is known that a method to join a plurality of ceramic members formed of a silicon carbide-silicon composite sintered body or the like via a silicon carbide-silicon composite material layer (joining layer). Also, after a plurality of ceramic members are joined together with an organic resin-based adhesive, the joined part is impregnated with molten silicon. The joining layer is formed of silicon carbide particles, which are based on reaction between carbon in the organic resin and the molten silicon, and a silicon phase existing in interstices among the particles.
Further, after a plurality of ceramic members are joined with an adhesive containing a silicon carbide powder, a carbon powder, and an organic resin, the joined part is impregnated with molten silicon. In this case, in addition to silicon carbide particles based on the silicon carbide powder in the adhesive, the joining layer contains silicon carbide particles based on reaction between carbon contents in the carbon powder and the organic resin and the molten silicon, and the silicon phase is made to exist in interstices among these silicon carbide particles. In either case, a thermosetting resin is used as the organic resin to be an adhering component and a viscous component in the adhesive.
By the joining method described above, a free silicon phase exists in interstices among the silicon carbide particles forming the joining layer (silicon carbide-silicon composite material layer), which improves denseness or mechanical properties of the joining layer. Thus, joining strength among a plurality of ceramic members can be enhanced. However, it is known that, since the adhesive use a thermosetting resin, it is necessary to cure the thermosetting resin by heat treatment when obtaining a shaped product made by preliminarily joining a plurality of ceramic members (a shaped product before being impregnated with molten silicon). The thermosetting resin becomes soft once while being heated, and thus it is possible that a displacement or the like occurs in a joined part of the shaped product, making it unable to keep its intended shape.
Therefore, so as to keep the shape of a preliminarily shaped product or, in particular, the shape of a joined part by using an adhesive during curing treatment for the thermosetting resin, it is necessary to fix the preliminary shaped product with a jig. The jig to fix the preliminary shaped product needs to be prepared corresponding to the shapes and sizes of various types of parts, and thus becomes a main cause to increase manufacturing costs and the number of manufacturing processes of ceramic composite members such as joined members. Further, even when the preliminary shaped product is fixed with a jig, the thickness of the joined part may be uncontrollable, and dispersion in thickness of the final joining part may occur, which decreases material properties including joining strength.